Various systems have been suggested to date to enable the locating and tracking of stolen or missing vehicles. These systems are generally categorized in two groups, namely those which make use of existing police radio communication infrastructures and those which make use of existing cellular network infrastructures.
U.S. Pat. Nos. 4,818,998 and 4,908,629 which both issued to Apsell et al are directed to the former. That is, Apsell et al teach the use of an apparatus and method for tracking vehicles equipped with computer-registered transponders which may be located or tracked by appropriately equipped police direction-finding vehicles. The police tracking the stolen vehicles home in on periodic transponder reply radio transmissions which are activated by command activation signals.
The problem associated with such systems, is that special police radio infrastructures are required in order to track and locate the stolen vehicles. In addition, unless the police vehicle is located in the same general area as the stolen vehicle, it is unlikely that the stolen vehicle can be located in view of the limited range of transmission between the stolen vehicle and police vehicle as well as any broadcast towers used with this invention. Also, once a car is removed from a city provided with this infrastructure, it will likely never be found since the system operates solely in a city having the specified system.
Because of their wide service area, cellular networks offer advantages over the aforementioned tracking systems. A vehicle tracking system making use of a cellular network is disclosed in U.S. Pat. No. 5,299,132. In this system, a cellular telephone in a vehicle is interrogated to obtain location information received by the cellular phone in an overhead message stream transmitted from the cellular network. Once a reply to the interrogation is received at the host controller, the location of the vehicle is displayed. A microprocessor at the cellular phone checks the serial identification number and a database for dial-out procedure to the host controller upon being interrogated to obtain location information.
Yet another system for tracking vehicles which makes use of a cellular network is disclosed in U.S. Pat. No. 5,208,756. With this system, a small hidden device located in the vehicle is activated through DTMF signals transmitted from any telephone station. Upon activation, the device determines the power at which normally transmitted control channels are received from several base stations of the network. Based upon these determinations, the device then calculates the distance between the vehicle and each of the base stations and, using triangulation or arculation, determines the location of the vehicle. The location information is then transmitted through a voice synthesizer back to the telephone station from which the activation signal is received. The location information is also transmitted digitally to a central station where the position of the vehicle is displayed on a computer screen along with a graphical representation of a map of the region served by the cellular telephone network.
U.S. Pat. No. 5,218,367 makes use of the cellular network by sending an emergency message transmission to a remote monitoring station in the event a theft sensor is activated on the vehicle. The monitoring system then detects the cell site identification codes from adjacent cellular transmitter and provides a message including the vehicle identification, cell site identification and signal RSSI. A computer located at a central station then provides a determination of the location of the stolen vehicle based on the information received.
U.S. Pat. Nos. 5,055,851 and 4,891,650 make use of the cellular network in a similar fashion. That is, the stolen vehicle sends an identification code and RSSI level to the closest cell site. The active cell site which receives the information reports the theft to the cellular MTSO and the MTSO transmits the information to an alarm station which identifies the vehicle and cell site.
A problem associated with the aforementioned systems is that in most instances, cell sites located in metropolitan areas make use of low-powered 120.degree. directional antennas to cover a densely populated and developed area which may have a large number of buildings, highways, side streets, parking lots, garages and other facilities where the thief may be able to hide the vehicle. Thus, although the aforementioned systems may be able to locate the general location of the vehicle with respect to a cell site antenna, the probability of locating the vehicle in short order is still fairly small and mostly based on luck. Furthermore, cell sites located in urban areas cover very large areas with high-powered, omnidirectional antennas, making location finding even more difficult since the antennas are omnidirectional as opposed to sectorized. In both cases, buildings, underground parking lots, mountains and other obstacles often cause the towers to report false RSSI readings to the MTSO.
Yet another problem associated with the aforementioned systems is that most of the techniques require in some form or another modification to the existing cellular infrastructure software to enable a cellular service provider to track and monitor movement of a stolen vehicle. In most instances, cellular service providers are in the majority reluctant to make any modification to their software for the purpose of tracking stolen vehicles.
A need therefore exists for providing a vehicle tracking method and system using existing cellular network infrastructure which can overcome the problems associated with the prior art.
Accordingly, it is an object of the present invention to provide a vehicle tracking method and system which make use of the existing cellular network infrastructure, but wherein the cellular service provider is not required to modify its software in order to identify the general location of a stolen vehicle.
Another object of the present invention is to provide a vehicle tracking method and system which make use of the existing cellular network infrastructure, wherein a tracking vehicle making use of a radio signal direction finder is used to quickly obtain a more accurate indication of the location of the stolen vehicle can be obtained.
Another object of the present invention is to provide a vehicle tracking method and system which make use of the existing cellular network infrastructure, wherein a stolen vehicle can be tracked by keeping a voice channel open between the cellular network and a locating cellular transceiver installed in the stolen vehicle.
Yet another object of the present invention to provide a vehicle tracking method and system using the cellular network infrastructure, wherein the general location of the stolen vehicle can be determined by paging a cellular transceiver located in the stolen vehicle to permit identification by the MTSO of one or more cell sites located near the stolen vehicle and relaying the information to a tracking vehicle which makes use of a radio direction finder to obtain an accurate bearing on the location of the stolen vehicle.
Yet another object of the present invention to provide a vehicle tracking method and system which make use of the existing cellular network infrastructure, wherein the cellular transceiver which is installed in a vehicle that requires tracking, operates on a continuous standby mode for tracking its general location and is turned to an active mode when tracking of the vehicle is initiated.
Yet another object of the present invention is to provide a method and system of locating a stolen vehicle using existing cellular infrastructure, wherein a tracking vehicle provided with a radio direction finder can determine using a global positioning system receiver its location with respect to one or more cell sites identified as being close to said stolen vehicle such that the tracking vehicle can quickly travel to the area identified by the selected cell sites.
In accordance with an embodiment of the present invention, there is provided a method of locating a stolen vehicle provided with a locating cellular transceiver, using the existing cellular network infrastructure, comprising the steps of:
(a) receiving an indication that said vehicle has been stolen;
(b) paging said locating cellular transceiver;
(c) maintaining an open voice channel with said locating cellular transceiver of said stolen vehicle;
(d) estimating the coordinates of the vehicle location based on the location of a cell site communicating with said locating cellular transceiver;
(e) determining the location of a search vehicle with respect to said one or more cell sites;
(f) monitoring said open voice channel from said search vehicle; and
(g) locating said stolen vehicle based on the direction of arrival of RF signals emitted by said stolen vehicle and received at said search vehicle.
In accordance with a further embodiment of the invention, there is provided a system for locating a stolen vehicle provided with a locating cellular transceiver, said system operating using the existing cellular network infrastructure, comprising:
(a) means for receiving an indication that said vehicle has been stolen;
(b) means for paging said locating cellular transceiver;
(c) cellular radio means for maintaining an open voice channel with said locating cellular transceiver of said stolen vehicle;
(d) means for estimating the coordinates of the vehicle location based on the location of one or more cell sites communicating with said locating cellular transceiver;
(e) positioning means for determining the location of a search vehicle with respect to said one or more cell sites;
(f) radio means for monitoring said open voice channel from said search vehicle; and
(g) radio location finder means for locating said stolen vehicle based on the direction of arrival of RF signals emitted by said stolen vehicle and received at said search vehicle.